The present invention relates to a stress-at-work evaluating device and a stress-at-work evaluating method, and more particularly to a device for evaluating a stress of a subject at work.
A method using biological information, such as an electromyogram (EMG) or a brain wave, is known as a general technique for measuring the mental burden (stress) of a subject. The method using biological information frequently imparts some restriction on a subject and needs a relatively long recording time to analyze the acquired data. For this reason, the method cannot be used for evaluating the mental stress of a subject if the subject is not confined to bed (for example, JP 11-19075 A).
A person frequently suffers from great mental stress when he/she drives a vehicle (stress while working). The level of stress varies from person to person, and situations where the person suffers from stress vary from person to person. In a situation where riding in a vehicle is uncomfortable or controllability (steering performance) of the vehicle is poor, excessive strain is apt to occur in the driver. Such excess strain is likely to interfere with smooth driving, possibly causing an accident.
During the development and design of a vehicle etc., an electromyogram, which is easily measured and used, is obtained from myoelectric signals. These myoelectric signals show activities of muscles in parts of the human body, those muscles being heavily loaded during driving. By detecting myoelectric signals of muscles heavily burdened (i.e., muscles of the arms and feet), the mental stress of the subject driving the vehicle is directly evaluated.
When a human being suffers from mental stress, the muscle sustains excessive strain due to unintentional muscle activity. Accordingly, such mental stress can be measured by measuring the muscle's activity.
Activities of the arms and the feet, which are largely exercised in work such as driving a vehicle, are acquired in the form of an electromyogram (EMG), whereby activity of the muscles at work is measured and stress on the human body is judged in conventional cases. However, a method of objectively expressing a person's mental burden (mental stress) while working using an EMG has not been found yet.
In an EMG representing the activities of the muscles at work such as the arm and the foot, a myoelectric signal indicating the muscle activities brought on by work such as driving a vehicle and a myoelectric signal representing the “excessive muscle strain” caused by stress are superposed on each other. It is thus difficult to discriminate the muscle activity due to driving from the muscle activity due to mental stress.
Methods using biological information other than an EMG often impart some restriction on a subject and need a relatively long recording time to analyze the acquired data. Therefore, it is difficult to correctly evaluate mental stress at work.
During conventional development and design of a vehicle etc., items relating to a driver's mental burden (mental stress), such as riding comfort and controllability (steering performance), are merely described subjectively in terms of the driver's opinion about driving the vehicle. As a result, it is impossible to objectively judge mental stress in the driver while driving.